It is well known that the performance of an electrostatic precipitator is highly dependent on the efficiency of particulate collection in the precipitator. Particularly, high voltage discharge electrodes located between parallel collector plates in a precipitator electrically charge particulate laden gas flowing through the precipitator. The electrically charged particulates are attracted to, and collected by, oppositely charged collecting surfaces of the collector plates. The cleaned gas may then be further processed or safely discharged to the atmosphere.
The maximum operating voltage of each electrode in a precipitator is determined by the distance from that electrode to the collecting surface. Since it is conventional for the electrodes in a precipitator to bisect the annular distance between collector plates, maximum operating voltage is likewise determined by the distance between collector plates. The greater this distance, the greater the maximum operating voltage. Because the implied voltage within the precipitator is reduced as the collector plate bends closer to the electrode it is desirable for collector plates, once they are positioned within a precipitator, to be sturdy and rigid and to resist lateral movement.
Many attempts have been made to produce a collector plate that will resist deflection. For instance, as shown in U.S. Pat. Nos. 2,815,824 and 2,826,262, it is known to place a series of triangular-shaped baffles along the length of a collector plate to increase the vertical stiffness of the plate. While such an arrangement aids in preventing plate deflection, manufacturing is expensive and cumbersome. More modernly, as shown in the preferred embodiment of the present invention, dimples or bent portions along the vertical length of a collector plate are utilized to increase the rigidity of the plate. Additionally, reducing the size of the collector plate is known to aid in the prevention of plate deflection.
It is also known that increasing the cross-sectional dimension of the ends of a collector plate provides for a more rigid structure and helps reduce collector plate deflection. Particularly, it has been found that the rigidity of a collector plate increases as the cross-sectional area of the ends of the plate increases. Mechanically rolling each end of a collector plate is a commonly used method to increase its cross-sectional area. It is believed that all prior art collector plates having rolled or bent ends, while varying in design, have been asymmetrical about the central longitudinal plane of the collector plate. For instance, it is common to roll the end portion of a collector plate to provide a semi-circular or similar embodiment at the ends of the collector plate thereby leaving an open portion at one side of the plate at each end of the plate.
Such prior art collector plates, while reducing plate deflection, have more mass resulting from the rolling process aligned on one side of a central longitudinal plane of the plate than on the opposite side of this plane. Therefore, these plates tend to bow or deflect to a greater extent towards the side of the plate having the least mass at its ends.
To overcome this problem, it is common practice in the precipitator art to vertically align these asymmetrical plates in rows within the precipitator in an alternating fashion. In other words, a first plate in a series of plates will have a greater mass at its ends on a first side of the plate. As a result, the plate will tend to bow in a first direction. The next plate, however, will be reversed so that the greater amount of mass at its ends are located on the side of the plate that is opposite to the arrangement of the first plate. Accordingly, this second plate will tend to deflect in the opposite direction. This arrangement is repeated throughout the precipitator.
While the foregoing described alternating collector plate arrangement reduces the ill-effects of collector plate deflection, it illustrates the design problem inherent in the collector plates described. Moreover, deflection is not prevented, but only compensated. Additionally, collector plates of this type tend to bow during rapping for cleaning of the plates.
Additionally, a further problem exists with collector plates having ends with increased cross-sectional areas. As discussed, it is desirable to prevent deflection of the plate into the electrical discharge field created by the voltage discharge electrodes. However, as the cross-sectional area of the end of a plate is increased thereby increasing the rigidity of the plate, the end of the plate itself may impinge on the electric field being generated by the electrode, thereby reducing the implied voltage within the precipitator and hindering collection efficiency.
Additionally, the opened-ends of these prior art devices causes the distance from electrode to plate to be highly irregular which, in turn, causes instability in the electric field. Instability in the electric field limits the maximum average power input to the precipitator. Accordingly, deflection of collector plates continues to be an on-going problem in the precipitator art.